Facilities, such as, hospitals, universities, research laboratories and nuclear power reactors, that use radioactive material, can have planned or unplanned, continuous or batch discharges of radioactive material to the environment. Much of this material is in the form of a liquid. These releases can result in surface water, ground water and drinking water contamination.
Radiochemical analysis methods are known and used to quantify the level of contamination. Using these methods, the contaminant is either co-precipitated with a carrier or concentrated on an ion-exchange or extraction chromatographic material. In the ion-exchange/extraction chromatography method, the contaminant is eluted from the material and concentrated into a small volume. This concentrated volume of solution is processed for quantification using a radiation sensor.
Advances have been made using extraction chromatography that lowered the sample analysis cost and time necessary for the analysis. However, the extraction chromatography augmented traditional methods are still time consuming and expensive, and do not facilitate real-time on-line analysis.
One alternative to traditional radiochemical methods, is on-line real-time flow monitoring. In one example of such an on-line arrangement, a flow cell sensor for real-time quantification is preceded by the elemental separation of a contaminant through high-performance liquid chromatography. The radioactive effluent is then separately characterized by a flow cell sensor. In this application, the counting time, that is the length of time that the sensor is permitted to count radioactive disintegrations from the material, is quite short, on the order of 20 to 25 seconds. When high-performance liquid chromatography is used to concentrate the contaminant, the resulting detection limit for a 10 milliliter sample of 500 bequerels/liter (Bq/L) for alpha-emitting nuclides, Reboul, et al., J. Health Physics, 68:585-89 (1995), and 350 Bq/L for high-energy beta-emitting nuclides was achieved, Reboul, et al., Radioactivity and Radiochemistry, 5:42-49 (1994). However, the above technique requires substantial concentration of the contaminant before it can be used for near real-time monitoring, and the separation and detection systems can be quite costly.
Continuous water monitors for effluent monitoring have been developed that quantify the gamma ray-emitting isotopes with a detection limit of about 0.2 Bq/L for a 60 minute counting time, Bronson, et al., 27.sup.th Midyear Topical Meeting of the Health Physics Society, Feb. 13-17, 1994. Two tritium (low-energy beta-emitter) flow cell sensors are known that monitor effluent at the Department of Energy Savanna River Site. The sensors have achievable detection limits, for a 60 minute counting time, of about 750 Bq/L for the heterogeneous flow cell sensor, Hofstetter, et al., Westinghouse Savannah River Co. WSRC-MS-92-163, and about 7 Bq/L for the homogeneous flow cell sensor, Sigg et al., Nucl. Instr. And Meth. In Phys. Res., A353:494-98 (1994).
These effluent monitoring sensors have reasonably low detection limits because a long counting time is used, which is achieved through a physical hold-up system. Although this hold-up system functions well for providing accurate radiation detection, it requires large physical samples to achieve low detection limits. Moreover, requiring long physical or chemical hold-up times prior to quantification is completely counter to the desire to provide on-line, real-time or near real-time detection of effluent stream contamination.
Concentration and quantification of contaminants in an aqueous stream using ion-exchange material has been achieved. Europium-doped calcium fluoride has also been investigated as a dual-purpose sensor material. DeVol, et al., IEEE Trans. Nucl. Sci., Vol. 43, No. 3:1310-15 (1996); Branton, Clemson University, Private Communication (1996). However, high selectivity has not been achieved using this material.
Attempts have also been made to provide an organic extractant on nonporous scintillator supports, such as cerium-doped lithium silicate glass beads, scintillating polyvinyltoluene beads, and the aforementioned europium-doped calcium fluoride crystals. The physical properties of these nonporous media were quite undesirable in that the resulting medium was not in a free-flowing or substantially free-flowing physical form. Rather, these non-porous media were a "sticky" glue-like suspension of the nonporous media in a viscous liquid carrier, which was difficult to handle and created problems in properly packing columns for use.
Accordingly, there exists a need for a dual-purpose extraction-scintillation medium that is highly chemically selective in extraction of the analyte of interest, is in a free-flowing or substantially free-flowing physical form, and is used in a radio-chemical sensor to provide on-line, real-time or near real-time detection of the sorbed analyte. Desirably, such an extraction-scintillation medium further includes the light output characteristics necessary for a successful scintillation medium.